High power diesel engines must meet increasingly stringent emission regulations for smoke values (i.e. white smoke or black smoke) and nitrogen oxides (NOx) values in various jurisdictions, such as EPA Tier 4 requirements in the United States. High power diesel engines often utilize high injection pressure in order to meet these requirements. At the same time, high power diesel engines are designed with large bore cylinders to produce high power output. The large bore cylinders are typically paired with injectors having nozzle sac volume to mitigate unacceptable smoke values at typical engine operating points (i.e. a typical engine speed and load) and high-pressure fuel injection systems to mitigate NOx emissions.
A typical high power diesel engine responds to low engine load by delivering a lower quantity of fuel to reduce power output. With lower quantities of fuel, injectors with large injector hole diameters and nozzle sac volume are difficult to control, resulting in poor combustion characteristics, such as poor fuel spray characteristics leading to increased smoke value.
Adding an engine exhaust aftertreatment system, such as a diesel particulate filter (DPF), to a high power diesel engine system can reduce smoke value. However, DPFs add cost, complexity, and potential for failure. For example, to prevent plugging and failure, a DPF requires a regeneration process, which requires higher fuel consumption, complex control algorithms, and more sensors.
Instead of an aftertreatment system, altering nozzle geometry, such as removing or reducing nozzle sac volume from the injectors, can improve fuel spray characteristics at lower engine loads. However, without nozzle sac volume, injectors would experience excessive nozzle cavitation and severely reduced nozzle life due to high pressure fueling typically used to meet NOx emission requirements.
There exists a continuing need to reliably reduce smoke value for high power diesel engines with nozzle sac volume, especially for low engine load conditions.